1. Field
This invention pertains to milling wheels for grain and is particularly directed to a matched pair of such wheels suitable for home grain mills.
2. State of the Art
A large variety of hand-powered and electrical-powered home grain mills is known. Many types and styles of milling wheels have been developed for use in such mills. Some of the milling wheels known to the prior art are constructed entirely of metal, but such wheels are generally not preferred because of the preference for stone ground flour. Milling wheels with stone or cast stone grinding surfaces have been of two types. Some such wheels are cast entirely from ceramic materials. Exemplary of such milling wheels is the matched set disclosed in U.S. Pat. No. 3,688,996. Ceramic wheels of this type produce excellent flour but have attendant disadvantages associated with the extremely poor heat conductivity of the ceramic material from which they are constructed. As a consequence, the grinding surface becomes unduly hot, tending to scorch the flour produced, particularly when wet grain is milled. Moreover, because heat is not readily radiated from the stone surfaces, a large quantity of heat is transferred from the rotor stone into the driven shaft to which it is mounted, thereby causing the shaft to expand. This expansion tends to decrease the spacing between the rotor and stator stones, thereby causing the stones to jam or overload the motor.
Efforts have been made to solve some of the problems associated with the poor heat conductivity of cast stone wheels through the expedient of attaching a cast stone ring to a metallic center. Such efforts have heretofore been unsatisfactory, both because of the relatively large proportion of stone in the composite wheel and because of the difficulties associated with achieving a balanced rotor and with maintaining good alignment between the grinding surface and the axis of the metallic insert.
There thus remains a need for a composite matched set of milling wheels with a stone grinding interface, good heat conductivity and balance, efficient milling characteristics and reliable alignment capabilities.